1. Technical Field
The present invention relates to a method of forming a thin film.
2. Related Art
As the method of forming a thin film, a spin coating method, a flexographic printing method, or the like have been generally used. On the contrary, a method of forming a thin film using a droplet discharging method effective for the reduction of the amount of consumed ink and the reduction of the number of steps have been recently wide-spreading. In such a method of forming a thin film using the droplet discharging method, the thin film is formed by discharging a plurality of droplets, ink (a liquid material) being as the droplet, to dispose and by drying this disposed ink thereby to remove the solvent within the ink.
However, in the method of forming a thin film using such a droplet discharging method, at the time of drying the ink disposed by discharging a plurality of droplets, the drying rate differs between the ink at the edge of a thin film and the ink in the center portion of the thin film. More particularly, the ink at the edge of the thin film dries at a higher speed than the ink in the center portion of the thin film. For this reason, in the step of drying the ink, the solid portion within the ink will flow to the edge where the drying rate is high, and as a result the thin film the edge of which is raised will be formed.
Such a thin film the edge of which is raised does not have a uniform film thickness, and therefore does not have a uniform functionality over the entire surface. For this reason, for example, when forming, by the method of forming a thin film using the droplet discharging method, an orientation film and an overcoating film of a liquid crystal display device which requires especially the uniformity of the film thickness in order to attain a higher quality, a problem will occur that the film thicknesses of the orientation film and the overcoating material are not made uniform, and thus the desired functionalities of the orientation film and the overcoating material are not obtained.
In order to solve such a problem, it is conceivable that the raising portion at the thin film edge is suppressed by applying the technique described in Japanese Unexamined Patent Publication No. 2001-170546 and giving a temperature gradient to the substrate, thereby controlling the drying rate at the edge and in the center portion of the thin film to make the drying rate equal between at the edge and in the center portion of the thin film.
Japanese Unexamined Patent Publication No. 2001-170546 is an example of related art.
However, when forming a thin film with the film thickness of the order of Å like the orientation film, the ink will evaporate at the time of having given a temperature gradient to the substrate, and thus the ink will dry to solidify before a leveling effect of the ink occurs. Moreover, the substrate having a temperature gradient will make non-uniform the temperature distribution in the same film surface of the ink which is discharge-disposed in the substrate. Accordingly, when using a polymer ink or a pigment ink as the ink, the kinetic conditions of the particles within the ink will change, and thus irregularity in the film will likely occur after having dried the ink.